The development of fuel cells as replacements for batteries in portable electronic devices, including many popular consumer electronics such as personal data assistants, cellular phones, and laptop computers, is dependent on finding a convenient and safe hydrogen source. The technology to create small-scale systems for hydrogen supply, storage, and delivery has not yet matched the advancements in miniaturization achieved with PEM fuel cells.
A hydrogen fuel source for small applications needs to have a compact, lightweight construction, should contain a fuel with a high gravimetric storage density, and must operate in many orientations. Additionally, it should be easy to match control of the system's hydrogen flow rate and pressure to the operating demands of the fuel cell.
A hydrogen fuel source in liquid form is ideal for small hydrogen generation applications as it is readily adaptable for use with a small fuel tank filled with the liquid fuel. The hydrogen generated may be supplied to a fuel cell for the generation of electricity. This form of electrical generation is portable and, therefore, is oftentimes preferable to the generation of electricity using a rechargeable battery which must be periodically connected to an AC electric supply or the like for battery recharging. The existing hydrogen storage options, which include compressed and liquid hydrogen, hydrided metal alloys, and carbon nanotubes, have characteristics which complicate their use in small consumer applications. For instance, compressed hydrogen and liquid hydrogen require heavy tanks and regulators for storage and delivery, metal hydrides require added heat to release their stored hydrogen, and carbon nanotube systems must be kept pressurized.
Alternatives for hydrogen storage and generation include the class of compounds known as chemical hydrides, such as the alkali metal hydrides, the alkali metal aluminum hydrides, and the alkali metal borohydrides. The hydrolysis reactions of many complex metal hydrides, including sodium borohydride (NaBH4), have commonly been used for the generation of hydrogen gas.
Sodium borohydride can be dissolved in alkaline water solutions with virtually no reaction. Furthermore, aqueous sodium borohydride fuel solutions are non-volatile and will not burn. This imparts handling and transport ease both in the bulk sense and within the hydrogen generator itself.
In those applications where a steady and constant supply of hydrogen is required, it is possible to construct hydrogen generation apparatus that control the contact of a catalyst with the hydride fuel. Such generators typically use a two-tank design, one for fuel and the other for the borate product. Hydrogen generation reaction takes place in a third chamber that contains a metal catalyst and connects the two tanks. However, such two-tank designs are not typically directionally independent and are not amenable to miniaturization.
An additional alternative for hydrogen storage and generation is the use of liquid hydrocarbons, including alcohols such as methanol and cyclohexanes. In the presence of appropriate catalysts, these compounds can be reformed to produce hydrogen.
The object of the current invention is a compact, self-regulating orientation-independent hydrogen generation system based on the catalytic hydrolysis and/or dehydrogenation of a liquid fuel, such as a liquid hydrocarbon fuel or as a chemical hydride solution. Contact of these fuels with a catalyst will produce hydrogen.